Formaldehyde modification of cellulose conducted in the presence of a stiffening agent and a lewis acid metallic salt



Patented Sept. 27, 1966 FORMALDEHYDE MODIFICATION OF CELLU- LOSE CONDUCTED IN THE PRESENCE OF A STIFFENING AGENT AND A LEWIS ACID ME- TALLIC SALT George C. Daul and Thomas F. Drake, Mobile, and Marshall W. Duke, Daphne, Ala., assignors, by mesne assignments, to Courtaulds, Limited, London, England, a British company No Drawing. Filed June 2, 1961, Ser. No. 114,313

15 Claims. (Cl. 8-115.6)

This application relates to a process for improving the properties of cellulosic textile materials and especially to a process for imparting permanent wash-wear properties to said materials.

The demand for Wash-wear fabrics has increased greatly in recent years. Broadly speaking, Wash-wear fabrics are those which after Washing and drying by conventional methods, recover or retain an ironed appearance Without pressing. An index to the wash-wear properties of a given fabric is its crease recovery angle, as defined in ASTM Designation: D1295-53T.

Various processes have been proposed for imparting suitable crease recovery properties to cellulosic textiles. In the copending application of Daul and Drake, Serial No. 81,956, filed January 11, 1961 (which is a continuation-in-part of applications SerialNos. 51,781, filed August 25, 1960, 38,418, filed June 24, 1960, and 792,696, filed February 12, 1959), there is described a process for cross linking cellulose with formaldehyde using as the curing agent a metallic salt which is a Lewis acid in the solid state. Preferably the formaldehyde and curing agent are applied at pH or above. By means of this process it is possible to cross link the cellulose wit-h relatively little adverse effect on its physical properties, especially its tensile strength, a drawback which had blocked widespread use of prior formaldehyde processes.

Cellulosic textiles treated according to the above process have improved dry crease recovery properties, i.e. when Washed and allowed to drip-dry, in an unrumpled state they assume a fresh, ironed appearance. However, unless the amount of formaldehyde bound to the fiber is very great, good wet crease recovery properties cannot be obtained, i.e. if washed and spun-dried so that they are dried in a rumpled state, they will not present an ironed appearance. Since many homes are equipped with mechanical driers it is important that clothes be spin-dryable and to get this effect both wet and dry crease recovery properties must be imparted. This problem has not gone unrecognized and several solutions have been offered to overcome it. One of these involves treating the cellulose with formaldehyde and a strong acid so that reaction is effected while the fabric is wet. with an aqueous solution of dichloropropanol and then storing the fabric for an extended time in a closed container. These processes are awkward to employ ind-"ustrially, use expensive reagents and in some cases cause very serious damage to the textile material.

From very early times the properties of textiles have been modified by applying stiifening agents. Starch is probably the oldest of such materials but many more easily spring to mind. Conventionally these stiffeners have been used for temporary effects which are lost in large measure after a single wash. It has been suggested that their permanency can be enhanced by applying them in the presence of formaldehyde. However, in such processes the treating conditions have been such that the amount of formaldehyde bound to the fabric was less than that necessary for improved crease recovery.

Another process involves impregnating the fabric It has now been found that the wet crease recovery of a fabric is a function of the dry stiffness of the fabric and that 'by applying any of the well known stiifeners which are capable of reacting with formaldehyde, to a cellulose fabric and applying formaldehyde to the fabric using the technique described in the Daul et al. applications mentioned above, it is possible to obtain fabrics having excellent wet and dry crease recovery properties, thus meeting both major requirements for wash-wear textiles.

The invention accordingly envisions a method for imparting wet and dry crease recovery properties to cellulosic textiles which comprises impregnating said textiles with formaldehyde, with at least 0.0030 mol, per g. of cellulose, of a curing agent which is a metallic salt and a Lewis acid in the solid state and which is water soluble to the extent of at least 0.03 mol per liter at 20 C. and pH 5, and a polymeric film forming stifiening material capable of reacting with formaldehyde, said impregnation with formaldehyde and metallic salt being effected in the presence of water at a pH of at least 5, and curing the impregnated material to cross link the cellulose and to bind the film forming material to the cellulose.

The invention can be applied to any variety of cellulosic fabrics, woven fabrics, knitted fabrics, the so-called no-Woven fabrics or even paper. The fabrics may consist wholly of cellulose fiber or in part of cellulose fibers and in part of fibers of other kinds, for example, cellulose acetate (acetone-soluble cellulose acetate or cellulose triacetate) fibers, fibers of synthetic linear polymers, for example of polyamides, such as nylon 6 or nylon 66, fibers of polyesters, for example polyethylene terephthalate, or fibers of addition polymers derived from acrylonitrile. Preferably when blends are treated, the cellulose fibers comprise at least 35% by weight of the blend.

If desired, the celluose, prior to treating, may have been dyed with any one of many common dyes, without adverse effect.

The formaldehyde used may be added to the treating solution as the normal 40% aqueous commercial solution. Other sources, e.g. paraformaldehyde, may, however, be used as desired.

As noted above, the curing agent should be a metallic salt which is a Lewis acid.

In determining whether any given salt is a Lewis acid,

the procedure described by Walling, JACS 72, pp. 1164- 1168 and Pines and Haag, JACS, 82, pp. 2471-2483, may be used. A particularly suitable test is to take a small quantity of the salt, dried to remove surface moisture, and allow it to stand overnight with a solution of the leuco base of Malachite Green (4,4-di(dimethylamino)- triphenyl methane) in a dry, non-polar solvent such as cyclohexane or isooctane. The development of a green color at the salt surface indicates that the salt is a Lewis acid. An alternative test may be based on the response of a compound to an indicator such as Methyl Red (whose range in aqueous solution is pH 4.46.2) under the conditions described by Walling (72 JACS, 11164). Indicators such as Methyl Red have the drawback of giving positive reactions in the presence of traces of acid (in the classical sense). On the other hand, the Malachite Green leuco base reaction appears to be inhibited by traces of classical acids.

In addition to being a Lewis acid, the curing agent should preferably be soluble and form no precipitate in aqueous solution at pH 5 at concentrations of at least 0.03 mol/liter at 20 C. For reasons explained more fully below, solutions at pH 6 or above are highly desirable for cotton and, therefore, when cotton is to be treated, the curing agent should be soluble at that pH.

Salts which remain soluble at higher pH are, of course,

more advantageous. Obviously, salts which are highly colored or highly toxic or become so during the process are undesirable.

Salts which meet these qualifications are in general those in which the metal is bivalent and belongs to Group II of the periodic table and the acid radical is that of a strong monobasic acid which is at least 50% ionized in normal aqueous solution at 18 C., such as hydrochloric, hydrobromic, hydriodic, nitric, perchloric and thi-ocyanic acids. Of most interest are salts of calcium, magnesium, strontium, barium and zinc. .Ex-amples of suitable salts would include CaCl CaBr Cal Ca(NO Ca(SCN) 3)2 2: 2 Z: ZHCIZ and Zn(NO as well as SrC'l Bacl and CdCl ZnSO may also be employed. Either the anhydrous salt or a hydrate may be used, as may mixtures of salts. .Generally the magnesium salts are preferred as being less acidic (in the classical sense) than the zinc salts and more effective (as curing agents) than the other salts mentioned; The magnesium halides are especially favored and of these, magnesium chloride is outstanding.

Magnesium chloride is of exceptional value in the present process for several reasons. First, it is stable in solutions with formaldehyde at pH up to about 9.- This enables even the most sensitive cellulose material to be impregnated and dried with minimal damage. Moreover, magnesium chloride has a very pronounced effect in lowering the vapor pressure of formaldehyde, possibly as the result of a complex formation. This tends to prevent loss of formaldehyde during curing, increasing the efficiency of the process.

The stiifeners which may be employed in the present invention include virtually all stiffeners employed in the textile industry, provided they are capable of reaction with formaldehyde. They are in general organic film forming polymeric materials having one or more reactive hydroxyl (-OH) or amino (NH groups per molecule. A list of such stiifeners would include starch, starch derivatives such as hydroxyethyl starch, carboxymethyl starch, oxidized starches, hydrolysed starches and chemically modified starches such as acylated stare-hes, and alky: lated starches. The list would further include dextran, dextran derivatives, dextrin, gelatin, natural gums of various sorts such as gum arabic,,gum tragacanth, and locust beau gum, casein, soybean protein, albumin and algin. Synthetic stiffeners are also useful, such as polyvinyl alcohol, polyacrylamide, cellulose derivatives including ethers such as hydroxyethyl cellulose, methyl cellulose and carboxy methyl cellulose. soluble vinyl ethers may also be used such as polyvinyl methyl ether.

The manner in which the formaldehyde and stiffeners are applied to the fabric is not especially importantprm vided that the stiffener is deposited on the fabric before the formaldehyde-cellulose reaction is perfected. Whatever technique is used to apply the formaldehyde, catalyst and stifiener to the fabric, it is essential that at least 0.03 mol of curing agent, per 100 g. of cellulose is deposited on the fabric and preferably between about 0.10 and about 0.45 mol, per 100 g. of cellulose. Suflicient formaldehyde is deposited so that after drying and curing between about 0.1 and about 3.0%, preferably between about 0.4 and about 3.0%, based on cellulose, is chemically bound to the cellulose.

The amount of stiffener deposited is normally in the range of 0.25 to 10.0% on the weight of cellulose.

Conveniently the formaldehyde, curing agent and stifl"- ener are applied from aqueous solutions. One solution maybe used for all of the treating agents, but in some instances it may be desirable to apply one or more of the formaldehyde, curing agent and stiffener in a separate solution. The solution or solutions mayv contain solvents other than water such as methanol or ethanol, but should contain at least 10% by weight water.

The concentration of formaldehyde in the treating solution may vary to a considerable extent depending on Certain waterwhether natural or regenerated cellulose is treated and.

on the structure of the fabric.

In generaLit has been found that the amountof curing agent deposited on the fiber and the etficiency of the curing agent in reacting unbound formaldehyde with cellulose are more significant than the concentration of formaldehyde in the solution, provided that enough formaldehyde .is present during curing to (furnish the desired. .quantity of formaldehyde required to be bound .to the. cellulose fort-he particular physical properties sought. An

dehyde by evaporation and are easier to work with from the point of View of operator health and comfort than the 1 more concentrated solutions prescribed in many prior processes. I 1

The concentration of curing agent may vary consider-. ably, depending on the agent.

between about 0.1 and about 0.45 g. mol/liter. However, it is the proportion of curing agent deposited on the fiber and to the extentthat the minimum amount of formalde hyde. must be present during curing, the molar ratio of agent to formaldehyde, which is significant.

The pH of the solution will depend onthe material being treated. Natural cellulose, suchas cotton, is'generally more sensitive to acid degradation and therefore when cotton is to be treated, a higher pH must be used than is necessary with-regenerated cellulose. Generally the treating solution pH should not be less than 5 .for regenerated cellulose and not less than 6 for cotton.

Some of the salts listed above when put into waterwith formaldehyde at use concentrations will not'give pI-Is in.

this range. When used in the present invention they are, therefore, preferably buffered, for example, withsodium carbonate, sodium bicarbonate, or sodium hydroxide,.to

a pH of at least 5, or at least 6 if cotton is to be treated.

While the upper pH limit is not especially critical, some of the salts most useful with the present invention will form precipitates at pHs above about 10.

The temperature of the treating solution is not especi-v ally significant. Roomtemperature is satisfactory, -al-. though lower temperatures may be used to prevent loss of formaldehyde; Normally, temperatures of say-715 C. to 50 C. are used. V

The concentration of stiffener may vary from say 0.25% to 10.0% by weight. Again it is.' the amount of stiffener applied .to the fabric rather than the concentration in the treating solution whichis important.

The actual manipulativetechniques used in applying Following impregnation, the material is dried at.say. 30110 C. for whatever time is requiredto reduce the.

moisture content to say 15% by weight of the bone dry material, and then cured by heating to temperatures from about. C. to about 180 C. for periods which may range from say 30 minutes to a few (say about 5 seconds.-

The temperatures and timefor curing must be carefully selected, having in mind the pH at which the treatment has been conducted and the curing agent used. Thus,.

where a pH of 5 has been used, curing must be conducted under mild conditions within the range set forth, i.e. if I a high temperature is used, a very short'time should be used, wit a long time. is used, the temperature should be Rayon Normally it will be bctween about 0.03 and about 0.90 g. mol/ liter; preferably weight of bone low, within the range set forth. If more rigorous curing conditions are employed, and the impregnation was at a low pH, there is danger of tendering the material.

By their nature most Lewis acids are capable of formpurposes of illustration only and are not to be taken as in any way restricting the invention beyond the scope of the appended claims.

Example 1 ihg hydrates and Sihhe the Present treatment ihvohfes P 5 This example illustrates a technique which may be used Phcation of aqueous Solutions, the clKing agent 1S 1101" to determine whether or not a given salt is a Lewis acid y deposited as a y With most Salts at least capable of cross-linking cellulose. a P Of the hydrate Water is evolved during chrhlg- It The leuco base of Malachite Green is purified by rehas been fo that during this Water evolution the peated recrystallization from absolute methanol until the lose-formaldehyde Teacttoh is inhibited least mark solid gives no green color when dissolved in glacial acetic Y depressed To avoid .Such inhibition or depression acid. A 0.5% by weight solution of the purified base in it is therefore desirable to conduct the curing at temperapure eyelohexane is then prepared, tures either above, below or between the range or ranges Approximately 5 1 grams f h l to h tested at which the Particular curing ageht used 10565 large is spread on a shallow dish and placed in a moving air amounts of water of hydrationstream at 80 C. for about 30 minutes. A small portion, Since it is desirable to conduct curing as expeditiously say 5 f the dried salt is then placed in a test tube as Passihle temperatures below dehydration temperature and 2 to 3 ml. of the leuco base-cyclohexane solution is are n usually employed. At the Same time eXtremely added to the tube. The mixture is allowed to stand for high temperatures are to be avoided for fear of damage 12 hours. The development of a green color on the surto the cellulose. face of the salt at the salt-liquid interface indicates that Because of these factors, salts which are Lewis acids the salt is a Lewis acid, and which can be heated at intermediate temperatures The results obtained with this test on a few salts are without water evolution are extremely desirable as curing listed in Table 1 below In h bl i i means agents, other things being equal. One of the properties that a green 1 developed that makes magnesium chloride especially attractive as a TABLE I curing agent in the present process is that although it S l Reaction loses some water at about 120 C., there is all intermedi- MgCl -6H O Positive, ate temperature range in which comparative y little Water A1 (SO D0, is evolved and the compound can therefore func i n fznusto Do, fectively as a curing agent without a prolonged curing time 0 50 or an excessively high temperature. c c

Zinc salts are enerally more likely o ca se gr (M10 50, Negative. tion than, say, magnesium salts and greater care must be (NH 1mm exerclsd 'curmg when the g adzmc mnipound' Similar results can be obtained using a 0.1% solution A the 39 treatment 15 i more gowns of Methyl Red in isooctane in place of the Malachite cunng conditions may be used, w1th1n the -range set Green leuco base solution forth, without adversely affecting the properties of the Care Should be taken See that prior to testing the b salts are dried to remove surface water, since this will l y the drymg i ail-ring Steps may 6 com- 40 interfere with the above tests. For example, if CaCl or bmedut asmgle tleatment Ffi' h h MgSO '7H O are permitted to stand in the air for sev- Fabrlc treated in accordancle1 wit :1 e invention lsf-cbareral h ours and tested Without drying, they will give no 'actenzfad mllch firmer and t t untreated a color. Yet if properly dried, as outlined above, they will and P firmness Permanent to h g' Moreover 1t give a positive test and, with proper curing temperatures, has Improved h recovery propertles Wet 4r' can be made to promote the formaldehyde-cellulose reac-' and dry states wlth respect to untreated fabric. Normally 0 tion the wet crease recovery angle is from to 150 higher Example 2 and the dry crease recovery .angle p 10 to 9 higher Samples of rayon fabric were treated with aqueous soluh those of untrefted fabnc' q the Physlcal Prop tions at pH 7 containing varying amounts of formaldeertles, such as tensile strength, may 1n some instances be 50 hyde MgC12 6H2O, and Starch squeezed to about 100% less than that of untreated fabric, this decrease is that pickup frame dried at for 10 minutes,*cured at Which always accompanies cross-linking and is not 160 C. for 5 minutes, washed and dried. The samples to a weakening tendering 0f the individual fibers Such were then tested for water irnbibition, formaldehyde conas would 066111 with prior formaldehyde treatments. The tent and crease recovery angle, dry and Wet, Results 3pcellulose chains are cross linked as indicated by the water pear in Table II.

TABLE II Deposition (Percent Wt. of Fabric) M 1 Fabric Properties hlgolgfi Hzo Sample per 100 g. Percent CRA (W+F)2 Starch MgC1z.6HzO HCHO Cell. Bound WI%1 Stifiness HCHO Dry Wet 0. 5 5. 5 5. 55 0. 0271 1. 0o 40. 2 231 251 0. 98' 1. 0 5. 5 5. 55 0. 0271 2. 20 41. 0 227 275 1. 05 a 2. 5 5. 5 5. 55 0. 0271 1. 76 39. 9 233 260 1. 14 4 (Control) 195 145 0. 50

l WI%=Water imbibition, percent. See Journal of the Society of Dyers and Colourists, Oct. 1948. p. 331. 2 CRA (W+F)=Crease recovery Angle (Warp & Filling), See ASTM Designation: D1295-53T. 3 Stifiness=Pierce Bending Length (inches). See ASTM Designation: D1388-55T.

imbibition which is normally on the order of 35 to and by the insolubility of the cellulose, after treatment, in cuprammoni-um hydroxide.

The invention will be further described with reference Example 3 The procedure of Example 2 was followed using various proportions of gelatin instead of starch. Results are to the following specific examples which are given for showninTable HI.

TABLE III Fabric Properties Stiffness Wet ORA" (W-i-F) Dry Percent Bound ECHO Mols Mg C12. 61120 per 100 g.

Cell.

Deposition (Percent Wt. of Fabric) Sample Gelatin MgClz.6HzO HCHO Example 4 Example 7 To demonstrate the laundering stability of finishes ace cording to. the invention, swatches of rayon fabric proc- The procedure of Example 1 was repeated using polyacrylamide. Results are shown in Table IV.

TABLE IV essed in accordance with the invention were washed with s LLLLLa m s mmnmmm w 22222 F v w W i t a W D. u m A finnmmm V. 122121 P R r c C D .1 r w F 384905 0 W mwwm44 20 mmo nmmssw m H 0 2 20 1 L HOG P E 0 211211 s mwwmww 5H0 000000 mwwm 0 00 000 M e m p \I 5555 0 %55S5: c b H L5 5 L5 5 n C M H 0 555555 W 2 4 5 5455 t H m i m m e g e M m W 550000 .3 yfl d 00122 4 0 1. P cm W Pa II I I I I I II I B 1 D II I I m I I II I S I II I u n 123456 7 Example 5 I The procedure of Example 1 was repeated using poly- Tide detergent for 10 cycles in a Frigidaire home washer. Vinyl alcohol- The results are Shown in Table The stiffness (bending length) was measured after the consideration of Table V will show that polyvinylalcohol being somewhat more flexible and elastic than, for exfirst, fifth and tenth wash and compared with the bendample, starch, does not give as high a stiffness-as starch mg length before'washing For the'sake of fuflher and will not impart as high a wet crease recovery angle as starch.

parison, the same amount of stiffener was applied with- TABLE V out formaldehyde cross linking. Results are shown 5 fififi 00 00 m t S 77 1 a mama F m w n W e w mmwm r. A V. 1222 P R r. .m C D r b a F 5996 220 6 I 5543 W mmo wwm W H 00 11 H0O P H 0 %nn 2 u mmmm M5 000 0 21 M 310 6 F b. 0 .m o mmm b H L3 5 7 n C M H m 0 5555 a t H 4:055 m I 2 r Q Q P g M m n 5555 w H w P D I e I 1 m s I I Example 6 The procedure of Example 1 was repeated using di- Table V aldehyde starch. The results are reported in Table VI.

TABLEVI V a 02 S 5735 w 0 2M0 n m I t. S I wwfln w 1.222 F .m w m M P e 317 w A mane P R w c C D n F 0488 m w%%% wmH 00 1I2 H0O P H Ov 2111 a mwww HM 0000 MMOm 00 00 .1110 .h r m. M .m o mmmw b H L3.5.7 a C F H m m m is t H 555 n 6 6 o c 1 r C e P g m PM I 5555 m S 2 2 2 2 m A e D D I 0 1 m I a I I I L TABLE v11 Pierce bending length Additive Percent after wash N o. Sample Additive percent WI% Bound HCHO 1 50.8 i 0.72 0.90 1.10 1.01 1.17 1 37.6 1.72 1. 23 1. 23 1.16 0. s6 1 No E6110 1.18 0.87 0.86 0.71 1 53 s 0.87 0.89 1. 43 1.34 1.41 1 41 6 1. 32 1.43 1.49 1.58 1.40 do 1 No HCHO 1.12 0.69 0.69 0. 64 Polyacrylarnide 1 0.71 1.68 1.62 1.66 1.58 -do 1 1.84 1.65 1.65 1.56 1.50 do 1 No HICHO 1.51 0.88 0.78 0.66

We claim: 7. The method claimed in claim 6 wherein the film 1. A method for improving the wet and dry crease forming material is starch. recovery properties of cellulose fabrics which comprises 8. The method claimed in claim 7 wherein the film impregnating said fabrics with formaldehyde, with at least forming material is gelatin. 0.03 mol, per 100 g. of cellulose, of a metallic salt which 9. The method claimed in claim 7 wherein the film is a Lewis acid in the solid state and which is water soluforming material is polyvinyl alcohol. ble to the extent of at least 0.03 mol/liter at 20 C. and 10. The method claimed in claim 7 wherein the film pH 5, and a polymeric film forming stiliening material forming material is polyacrylamid. capable of reacting with mormaldehyde, said impregna- 11. The method claimed in claim 7 wherein the filrn tion with formaldehyde and metallic salt being eifected in forming material is dialdehyde starch. the presence of water at a pH of at least 5, and curing the 12. A method for improving the wet and dry crease impregnated material to cross link the cellulose and to recovery properties of cellulose fabrics which comprises bond the film forming material to the cellulose. impregnating said fabrics with formaldehyde, with at 2. The method claimed in claim 1 wherein the metallic least 0.03 iIIl'Ol, per 100 g. of cellulose, of a salt of a Group salt is magnesium salt. II metal and a strong monobasic acid which is at least 3. The method claimed in claim 2 wherein the mag- 50% ionized in normal aqueous solution at 18 C. and nesium salt is magnesium chloride. With a polymeric film forming stiffening material selected 4. A method for improving the wet and dry crease from the group consisting of starch, starch derivatives, recovery properties of cellulose fabrics which comprises dextran, dextran derivatives, gelatin, natural gums, casein, impregnating said fabrics with formaldehyde, with at Soybean P albumin, 21121-11, P y y C l, P 3!- least about 0.03 mol, per 100 g. of cellulose, of a salt vinyl ethers, P y y and Gel-1111056 ethefs, Said selected fr m th lgl'oup consisting of magnesium chloriimpregnation with formaldehyde and salt being effected ide, magnesium bromide, magnesium iodide, magnesium in the Presenw Water 3 P at least about and nitrate, magnesium perchlorate, zinc nitrate, zinc chloricuring the impregnated material to cross-link the celluide, zinc sulfate, calcium chloride, calcium bromide, callose and to bond the film forming material to the cellulose.- cium iodide, calcium nitrate, calcium thiocyanate, barium 4.0 13! The method C a d in Claim 12 w r in the alt chloride, strontium chloride and cadmium chloride, and is amagnesium halidewith a polymeric film forming stiffening m t ri l bk; 14. The method claimed in claim 13 wherein the salt of reacting with formaldehyde, said impregnation with is magnesium chlol'ideformaldehyde and salt being effected in the presence of A method for improving the Wet and y 'cfease water at a pH of at least about 5, and curing the impregrecovery Properties 0f Cellulose fabrics Which Comprises nated material to cross-link the cellulose and to bond the impregnating Said fabrics with formaldehyde, With at least stiffening material to the cellulo 0.03 mol, per 100 g. of cellulose, of a salt selected from 5. A method for improving the dry and wet crease the gnOuP consisting magnesium chloride, magnesium recovery properties of cellulose fabrics which comprises bromide, magnesium iodide, magnesium flitratfi, impregnating cellulose fabric with formaldehyde, with at Ilfisillm Perchlorate, Z1110 nitrate. Zinc Chloride, Zinc $111- least 0.03 mol, per 100 g. of cellulose, of a salt of a Group fate, calcium chloride, calcium bromide, Calcium iodide, II metal and a strong monobasic acid which is at least calcium nitrate, calcium thiocyaflate, barium Chloride, 50% ionized in normal aqueous solution at 18 C., and strontium chloride and cadmium chloride, and with a with a polymeric film-formin tiff i material, Said polymeric film forming stiffening material selected from impregnation with formaldehyde and salt being effected the group consisting of starch. starch derivatives, \dextran, in the presence of water at a pH of at least 5; and curing dextran derivatives, gelatin, natural gums, casein, Y- the impregnated material to cross-link the cellulose and bean Protein, albumin, 'algil'l, P y y alcohol, P Y Y to bond the film forming material to the cellulose. 'f pqlyacrylamide, and Cellulose l a said P 6' A method f improving the dry and Wet Crease nation with formaldehyde and salt being eifected in the recovery properties of cellulose fabrics which comprises preslmce of Water at 3 P of at 1eas.t about and cunng impregnating said fabrics with formaldehyde, with at least the lmpregnated matellal to 9 the cellulose and 0.03 mol, per 100 of cellulose, of a metallic salt which to bond the film formmg material to the cellulose. is a Lewis acid in the solid state and which is water soluble to the extent of at least 0.03 moi/liter at 20 C. and References Clted by the Exammer pH 5, and with a polymeric film forming stifiening mate- UNITED STATES PATENTS rial selected from the group consisting f t h, t h 974,488 11/1910 Supf 106135 derivatives, dextran, dextran derivaties, gelatin, natural 1,506,013 8/1924 Lindauer 106135 gums, casein, soybean pr in, albumin, algin, polyvinyl gggigg Z1333 gig-g alcohol, 01 vin l ethers, ol ac d I r 1 a 111$ p y y p y rylaml e and cellulose 3,113,826 12/1963 Daul et a1. 8116.4

others, said impregnation with formaldehyde and metallic salt being effected in the presence of water at a pH of at least about 5, and curing the impregnated material to cross-link the cellulose and to bond the film forming material to the cellulose.

NORMAN G. TORCHIN, Primary Examiner.

MORRIS O. WOLK, Examiner.

H. WOLMAN, J C. CANNON, Assistant Examiners. 

1. A METHOD FOR IMPROVING THE WET AND DRY CREASE RECOVERY PROPERTIES OF CELLULOSE FABRICS WHICH COMPRISES IMPREGNATING SAID FABRICS WITH FROMALDEHYDE, WITH AT LEAST 0.03 MOL, PER 100 G. OF CELLULOSE, OF A METALLIC SALT WHICH IS A LEWIS ACID IN THE SOLID STATE AND WHICH IS WATER SOLUBLE TO THE EXTENT OF AT LEAST 0.03 MOL/LITER AT 20*C. AND PH 5, AND A POLYMERIC FILM FORMING STIFFENING MATERIAL CAPABLE OF REACTING WITH NORMALDEHYDE, SAID IMPREGNATION WITH FORMALDEHYDE AND METALLIC SALT BEING EFFECTED IN THE PRESENCE OF WATER AT A PH OF AT LEAST 5, AND CURING THE IMPREGNATED MATERIAL TO CROSS LINK THE CELLULOSE AND TO BOND THE FILM MATERIAL TO THE CELLULOSE. 